如何从.NET数据结构创建"锯齿状"对象的JSON数组

Question

作为LINQ-to-Entities投影的结果,我最终得到了一个List<ChartDataRecord>看起来像我手动创建它的情况:

List<ChartDataRecord> data = new List<ChartDataRecord>();
data.Add(new ChartDataRecord { date = 1370563200000, graph = "g0", value = 70 });
data.Add(new ChartDataRecord { date = 1370563200000, graph = "g1", value = 60 });
data.Add(new ChartDataRecord { date = 1370563200000, graph = "g2", value = 100 });
data.Add(new ChartDataRecord { date = 1370563260000, graph = "g0", value = 71 });
data.Add(new ChartDataRecord { date = 1370563260000, graph = "g2", value = 110 });
data.Add(new ChartDataRecord { date = 1370563320000, graph = "g0", value = 72 });
data.Add(new ChartDataRecord { date = 1370563320000, graph = "g1", value = 62 });
data.Add(new ChartDataRecord { date = 1370563320000, graph = "g2", value = 150 });

我正在使用的图表框架(amCharts)要求JSON数据提供程序的格式如下:

{
   "data": [
      { "date": 1370563200000, "g0": 70, "g1": 60, "g2": 100 },
      { "date": 1370563260000, "g0": 71, "g2": 110 },
      { "date": 1370563320000, "g0": 72, "g1": 62, "g2": 150 }
   ],
   ...other chart properties
}

将样本序列化List<ChartDataRecord>为此JSON结构的推荐方法是什么？Json.NET框架中是否有一些可以使这相当容易的东西？如果没有,这将如何手动完成？我应该使用更动态的数据结构List<ChartDataRecord>并尝试使用我的LINQ到实体查询来填充它吗？

Answer 1

您可以使用自定义转换器执行此操作,如下所示:

class ChartDataRecordCollectionConverter : JsonConverter
{
    /// <summary>
    /// Writes the JSON representation of the object.
    /// </summary>
    /// <param name="writer">The <see cref="T:Newtonsoft.Json.JsonWriter"/> to write to.</param><param name="value">The value.</param><param name="serializer">The calling serializer.</param>
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var set = (ChartDataRecordCollection) value;

        writer.WriteStartObject();
        writer.WritePropertyName("data");
        writer.WriteStartArray();

        //Group up the records in the collection by the 'date' property
        foreach (var record in set.GroupBy(x => x.date))
        {
            writer.WriteStartObject();

            writer.WritePropertyName("date");
            writer.WriteValue(record.Key);

            //Write the graph/value pairs as properties and values
            foreach (var part in record)
            {
                writer.WritePropertyName(part.graph);
                writer.WriteValue(part.value);
            }

            writer.WriteEndObject();
        }

        writer.WriteEndArray();
        writer.WriteEndObject();
    }

    /// <summary>
    /// Reads the JSON representation of the object.
    /// </summary>
    /// <param name="reader">The <see cref="T:Newtonsoft.Json.JsonReader"/> to read from.</param><param name="objectType">Type of the object.</param><param name="existingValue">The existing value of object being read.</param><param name="serializer">The calling serializer.</param>
    /// <returns>
    /// The object value.
    /// </returns>
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var result = new ChartDataRecordCollection();
        var obj = JObject.Load(reader);
        var container = obj["data"];

        //Examine each object in the array of values from the result
        foreach (JObject item in container)
        {
            //Get and store the date property
            var date = item["date"].Value<long>();

            //For each property that is not the date property on the object, construct a
            //  ChartDataRecord with the appropriate graph/value pair
            foreach (var property in item.Properties())
            {
                if (property.Name == "date")
                {
                    continue;
                }

                result.Add(new ChartDataRecord
                {
                    date = date,
                    graph = property.Name,
                    value = item[property.Name].Value<int>()
                });
            }
        }

        return result;
    }

    /// <summary>
    /// Determines whether this instance can convert the specified object type.
    /// </summary>
    /// <param name="objectType">Type of the object.</param>
    /// <returns>
    /// <c>true</c> if this instance can convert the specified object type; otherwise, <c>false</c>.
    /// </returns>
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof (ChartDataRecordCollection);
    }
}

此转换器将在List<ChartDataRecord>如此定义的集合类型包装上运行

[JsonConverter(typeof(ChartDataRecordCollectionConverter))]
public class ChartDataRecordCollection : List<ChartDataRecord>
{
    public ChartDataRecordCollection()
    {
    }

    public ChartDataRecordCollection(IEnumerable<ChartDataRecord> records)
    {
        AddRange(records);
    }
}

用法示例(和正确性证明):

public class ChartDataRecord
{
    public long date { get; set; }
    public string graph { get; set; }
    public int value { get; set; }

    public override bool Equals(object obj)
    {
        var o = (ChartDataRecord) obj;
        return o.date == date && o.graph == graph && o.value == value;
    }
}

...

static void Main(string[] args)
{
    var data = new List<ChartDataRecord>
    {
        new ChartDataRecord { date = 1370563200000, graph = "g0", value = 70 },
        new ChartDataRecord { date = 1370563200000, graph = "g1", value = 60 },
        new ChartDataRecord { date = 1370563200000, graph = "g2", value = 100 },
        new ChartDataRecord { date = 1370563260000, graph = "g0", value = 71 },
        new ChartDataRecord { date = 1370563260000, graph = "g2", value = 110 },
        new ChartDataRecord { date = 1370563320000, graph = "g0", value = 72 },
        new ChartDataRecord { date = 1370563320000, graph = "g1", value = 62 },
        new ChartDataRecord { date = 1370563320000, graph = "g2", value = 150 }
    };

    var records = new ChartDataRecordCollection(data);

    var result = JsonConvert.SerializeObject(records);
    Console.WriteLine(result);
    var test = JsonConvert.DeserializeObject<ChartDataRecordCollection>(result);
    Console.WriteLine(records.SequenceEqual(test));
    Console.ReadLine();
}

输出:

{"data":[{"date":1370563200000,"g0":70,"g1":60,"g2":100},{"date":1370563260000,"g0":71,"g2":110},{"date":1370563320000,"g0":72,"g1":62,"g2":150}]}
true